The present invention relates to winding machines. More particularly, this invention relates to a winding machine intended for winding continuous synthetic filaments such as those made of polyester and polyamide materials. In this specification, the term "filament" refers to a continuous mono-filament or multi-filament material.
In the production of a continuous synthetic filament, the filament is commonly drawn from a spinneret via a guide system to a wind-up device where it is formed into a package. The filament tension in the region of the spinneret is important to the filament producer because it affects the fineness (titer) of a filament and also the molecular orientation of the synthetic material. On the other hand, the filament tension in the region of the package is very relevant to the operation of the wind-up mechanism, since it has a substantial effect upon the quality of the package produced therewith and the performance of that package in subsequent filament treatment operations such as texturizing. It occurs only rarely, however, that an appropriate tension in the region of the spinneret is appropriate also for the production of a good quality package in the wind-up mechanism.
It has been common practice to provide a godet roller between the spinneret and the wind-up mechanism. The godet roller draws the filament from the spinneret at a tension appropriate to the spinneret and the wind-up mechanism can then take filament from the godet roller at a tension appropriate for winding. Thus, the godet roller "isolates" the tension conditions at the spinneret from those in the wind-up mechanism. However, the general trend is toward simplification of filament producing machinery and shortening of passage times between the spinneret and the wind-up. It is therefore desirable to eliminate the godet roller. The tension conditions in the region of the spinneret cannot be freely adjusted, since they are dependent upon the yarn type, desired titer, desired synthetic material etc., and it is therefore essential for the wind-up mechanism to accept the tension at the spinneret and to adjust the filament tension internally to an appropriate level for winding.
Attempts have already been made to cope with these problems. For example, U.S. Pat. No. 3,861,607 (DAS No. 2,435,898) describes a system which either includes a godet roller or which winds filament direct from the spinning nozzles. The U.S. patent describes a machine of a generally known type comprising a reciprocable thread guide from which the thread passes to a grooved roller before being laid onto the tube on which the package is being formed. The grooved roller is intended to perform two functions:
(a) at the end of each stroke of the reciprocable thread guide, the groove takes over guiding of the filament because it can produce a neater end on the package than the reversing thread guide, and
(b) the depth of the groove varies along the axial length of the roller to compensate for changes in the running length of the filament due to reciprocation of the thread guide transverse to the length of the filament.
The prior art device is concerned with the form of the groove most suitable for eliminating variations in filament tension introduced by the changes in running lengths. The U.S. Patent does refer to overall adjustment (or selective setting) of the filament tension at the package by selection of three factors, namely:
(a) contact angle between the grooved roller and the thread, preferably 90.degree.,
(b) use of a mat finish on the grooved roller surface and in the groove to provide a low coefficient of friction, and
(c) control of the peripheral velocity of the grooved roller.
The latter feature is used to permit adjustability of the thread tension of the filament leading to the winding package by adjustment of the peripheral velocity of the grooved roller.
There are two disadvantages in this method of adjustment, namely:
(a) the peripheral velocity of the grooved roller is not freely selectable over a wide range relative to the thread velocity; substantial variation in the velocity of the grooved roller will disturb the winding pattern given a constant thread speed, and
(b) adjustment of the peripheral velocity of the grooved roller relative to the filament speed can have only a limited effect upon the winding tension regardless of the degree of variation permitted in the said relative velocities.
The present invention is based on the discovery that, given a determinable minimum speed differential between the grooved roller and the filament, the filament tension downstream of the grooved roller is relatively insensitive to additional speed differential, but is relatively sensitive to variation in the contact length between the filament and the grooved roller, i.e. to the wrap angle of the filament around the grooved roller.
It is therefore an object of the present invention to make use of the above discovery by providing a winding machine which is inherently capable of being set to produce a required general level of winding tension despite substantial differences in tension of filaments which may be supplied to the machine in use.
The present invention therefore provides a winding machine for winding a filament into a package, comprising means for receiving and rotating a bobbin so as to wind a filament onto the bobbin, and tension control means adapted to be contacted by the filament with sliding friction therebetween, characterised in that the tension control means is adjustable to vary the contact length over which the filament will experience sliding friction in use.
The sliding friction may be between the filament and one or more bodies in the winding machine. Where a plurality of bodies are provided, the contact length may be varied by bringing bodies into and out of contact with the filament. Preferably, however, the sliding friction is between the filament and a single body which may be in the form of a roller, the wrap angle of the filament around the roller being adjustable to vary tension in the filament downstream of the roller. In the preferred embodiment, the roller is a grooved roller, known per se, defining a reversal pattern for the filament at the end of a package.
The machine may incorporate each or any of a number of other features known per se; for example, the means for receiving and rotating a bobbin may be adapted to wind a filament onto the bobbin at a substantially predetermined speed of the filament longitudinally of itself. For this purpose, this means may include a bobbin receiving shaft and a separate drive roll adapted for frictional contact with the bobbin/package. The path of the filament onto the package may then include a predetermined wrap of the filament around the drive roll before contact with the bobbin/package.
In an alternative arrangement, also known per se, the means for receiving and rotating the bobbin comprises a shaft adapted both to receive and drive the bobbin, means being provided to vary the angular velocity of the shaft during winding of a package to produce a substantially constant and predetermined peripheral velocity of the bobbin/package. The velocity varying means may include velocity sensing means, e.g. a friction roller engaging the surface of the bobbin/package, to sense the peripheral velocity of the bobbin/package, and velocity control means responsive to the velocity sensing means.
It is not an object of the present invention to define any particular shape of groove for compensating running length variations in the filament, and thus for eliminating variations in the overall level of tension set by the tension control means. Such groove shapes are already known and are, for example, the subject of U.S. Pat. No. 3,861,607 amongst others. In general, the selection of an appropriate groove shape is merely the application of conventional geometrical principles to the calculation of the running length of the filament between the last fixed filament guide and the point at which the filament reaches the package, the groove depth being adjusted to maintain this running length constant as far as possible and subject to other operating conditions. Grooved rollers having known groove shapes, or new shapes calculated in accordance with the above or any other principle for eliminating tension variation from a set value, can be used with the present invention. Means other than a grooved roller may be used for the same purpose. Alternatively, it may be found that tension variation caused by running length variation can be tolerated in some uses and then neither the grooved roller nor any other means is needed.
It will be appreciated that the formation of a groove of precisely controlled and continuously varying depth in the surface of a cylindrical roller is not an easy matter from a production viewpoint and this is a very substantial disadvantage of existing rollers. The disadvantages are still further exacerbated by groove crossings because the groove edges in the crossing regions must be very carefully formed to avoid interference with the smooth guiding of the filament in these regions. While grooves are virtually essential for guiding the filament in the reversal regions of the filament's traverse to form the package, it is desirable to avoid the use of grooves wherever possible.
A second aspect of the invention therefore provides, particularly but not exclusively for use in a winding machine according to the first aspect, a grooved roller for a filament winding machine of the type having a filament guide system comprising a roller and a reciprocable filament guide for traversing the filament along a bobbin on which a package is being formed. In addition, the roller has grooves in the reversal regions corresponding with the ends of a package. The roller has two smoothly tapering portions which taper in opposite directions outwardly from the mid-length of the roller towards respective ends thereof and which at their smaller ends join respective relatively enlarged portions. The grooves are provided in respective relatively enlarged portions and the base of each groove at each end thereof joins smoothly with the adjacent smoothly tapering portion.
The smoothly tapering portions may be joined by a portion of substantially cylindrical cross-section at and adjacent the mid-length of the roller. Preferably, the grooves are provided solely in the relatively enlarged portions, without extending into the smoothly tapered portions. Where they do extend onto the smoothly tapering portions, however, the use of crossing grooves is preferably avoided. The radial distance between the rotation axis of the roller and the base of each groove may vary along the length of the groove in a generally known manner.
The smoothly tapering portions are preferably frusto-conical and the relatively enlarged portions may have cylindrical cross-sections.